1. Field of the Invention
The present invention relates generally to mobile communications networks, and more specifically to a location update protocol for use in managing subscriber profile information associated with each of a plurality of mobile hosts of the network as the hosts move from one location in the network to another in a mobile communications network.
2. Description of the Prior Art
FIG. 1 shows a generalized block diagram of a conventional wireless mobile communications network at 10, the network 10 being operated in accordance with a prior art fully centralized cache management system for managing subscriber profile information associated with each of a plurality of subscribers of the network. The network 10 includes a central database system 14 (also commonly referred to as a network operating center, or an operations support system (OSS)) having a central server computer system 16, and a central database 18 communicatively coupled with the central server 16. The central database 18 provides a centralized cache for storing subscriber profiles associated with each of the subscribers, each profile including all information necessary for executing call-processing operations associated with the subscriber. The central database also provides for storing location register information associated with subscribers of the network, the location register information typically including a home location register database (HLR database) for storing location information associated with local registered subscribers of the network, and a visitor""s location register database (VLR database) for storing location information associated with roaming users of the network. When location information associated with a particular subscriber is required (e.g., for executing call processing functions), the central database system 14 is called upon to perform lookup functions in order to determine a profile and a current location of the subscriber in the network, the central database system then provides the location information along with the profile associated with the particular subscriber as further explained below. Typically, the central database system 14 is supported by a back office system that includes a subscriber management system, a billing system, and a network management system (not shown). Wireless communications networks, such as the network 10, typically operate in accordance with one of the wireless cellular communications standards such as GSM, CDMA, etc.
The wireless mobile network 10 further includes a plurality of base stations 24 communicatively coupled with each other, with the central database system 14, and with the transaction servers 20 via the backbone 22 of the network. Typically, each of the base stations 24 is communicatively coupled with a radio port (not shown) having an antenna 26, and is operative to communicate via wireless links with each of a plurality of mobile hosts 30 located within a coverage area 28 associated with the base station. Each of the mobile hosts 30 may be a cellular telephone handset, a personal digital assistant (PDA), or a lap top computer having wireless communication capabilities. As examples, a first one of the base stations 24 designated BASE_STATION_1 is associated with a first coverage area designated AREA_1, and a second one of the base stations designated BASE_STATION_2 is associated with a second coverage area designated AREA_2.
FIG. 2 shows a table diagram illustrating a global subscriber list at 40 including subscriber profile information associated with each subscriber of the network 10, the global subscriber list 40 being stored in the centralized database 18 (FIG. 1) of the central database system 14, and being managed in accordance with the prior art fully centralized data management system. The global subscriber list 40 includes a plurality of subscriber profile cache entries 42 each being associated with one of the subscribers of the network 10 (FIG. 1), and having: a subscriber key field 44 for storing a subscriber key value associated with one of the subscribers of the network; a base station location field 46 for storing a node identification value indicating an associated owner one of the base stations 24 (FIG. 1) which currently xe2x80x9cownsxe2x80x9d the associated subscriber profile as further explained below; and a profile information field 50 for storing the actual profile data associated with the subscriber.
Referring back to FIG. 1, when a subscriber initially activates one of the mobile hosts 30 within one of the coverage areas 28, a registration procedure is performed for xe2x80x9csigning onxe2x80x9d to the network. In accordance with the registration procedure, the host 30 transmits an associated link layer identifier (ID) to the local base station. The link layer ID typically includes a manufacturer identification value, which uniquely identifies the subscriber""s host device. When the base station receives the link layer ID, the base station must initially query the central database system 14 by sending a registration message to the central database system via one of the transaction servers 20 requesting access to a subscriber profile associated with the host. Typically, the network addresses of the transaction servers 20 are configured into the base stations 24. The registration message carries the link layer ID of the host, and the current location of the host which is indicated by the node ID value of the owner base station. The central server 14 is responsive to the registration message, and is operative to retrieve a subscriber profile matching the link layer ID from the central database 18, and is also operative to update the location field 46 (FIG. 2) of the corresponding subscriber profile cache entry to indicate the current location of the associated host in the event that the location has changed since a last transaction. So, the location of each subscriber is assumed to be the particular base station, which detected the sign-on, and the current owner of the profile is that particular base station.
In order to be able to correctly process calls to and from each of the mobile hosts 30 in the mobile communications network 10, a mechanism is provided to keep track of the location of subscribers. The location field 46 (FIG. 2) of each subscriber profile must be updated as the mobile hosts move within the network. As one of the hosts 30 moves from one of the coverage areas 28 to another, a handoff procedure is performed to transfer ownership of the associated subscriber profile (as well as control of communication between the host and other nodes of the network) from an old one of the base stations 24 to a new one of the base stations 24. Each of the base stations is operative to generate location update messages upon each hand-off that occurs, and is operative to provide the location update messages to the central server 16 for updating associated subscriber profiles. Each of the location update messages indicates a transfer of ownership of an associated one of the subscriber profiles.
In accordance with call processing operations in a fully centralized cache management system, when a call is initiated from a first one of the hosts 30 (a calling party) to a second one of the hosts (a called party), the base station currently associated with the calling party sends a query message to the central database 18, requesting profile and location information associated with the called party. The central database system 14 is responsive to the query messages, and operative to provide the requested profile information and location information to the base station associated with the calling party.
As an example of a call processing function, a calling party using HOST_A, currently located in AREA_1, initiates a call to a called party using a second host designated HOST_B that is currently located in AREA_2. BASE_STATION_1 which covers AREA_1 must determine a profile of the called party by sending a request for the profile of the subscriber associated with HOST_B to the central database system 14 via one of the transaction servers 20. The central database system 14 is responsive to the request and operative to search the global subscriber list 40 (FIG. 2) stored in the central database 18 using a lookup key which is typically the phone number associated with HOST_B. BASE_STATION_1 receives an answer from the central database system 14, the answer including the profile associated with HOST_B and also indicating that the current location of the called party is AREA_2 associated with BASE_STATION_2. Based on this information, BASE_STATION_1 sends call setup information to BASE_STATION_2 in order to try to initiate the call.
One problem associated with the fully centralized cache management approach to managing subscriber information in the network 10 is the high volume of data and messages which must be received and processed by the central server 16 of the central database system. In order to handle such a high volume of data processing, the central server 16 is typically implemented using a fault tolerant computer system, which provides a great amount of processing power. However, such systems are very expensive, and also very difficult to maintain.
Another problem associated with the use of the fully centralized approach to managing subscriber information in the network 10 is that call processing operations are highly dependent on communications between the central database system 14 and the base stations 24. While the transaction servers 20 provide redundancy and fault tolerance for communications between the central database system 14 and the base stations 24, the network is still overly dependent upon the central database system 14.
For example, if there is a communication failure between a particular one of the base stations 24 and the central database system 14, then the particular base station is isolated from the central database system, and as a result, all call set up operations fail for all subscribers located in the coverage area associated with the isolated base station. Even though the central database system 14 includes fault tolerant machines and communication links, this problem still arises.
In order to reduce the high dependency on communications between the base stations 24 and the central database system 14, some prior art mobile communications networks provide a partially decentralized cache management mechanism wherein cache entries associated with selected subscribers of the system are periodically provided from the central database system to their associated owner ones of the base stations 24. In such systems, the base stations include local databases (not shown) for storing locally owned subscriber profile entries. In such systems, the locally stored cache entries are aged out, that is deleted upon expiration of a set time period if the local entries are not refreshed at the end of the time period. A counter counts down to indicate termination of the period, and if the local entry is not refreshed at the end of the countdown period, the local entries are aged out. Problems also arise in this partially decentralized cache management system because if the locally stored information is not refreshed by the central database system (for example due to communication link failure between the particular one of the base stations and the central database system) after a certain amount of time, the local information is aged out and ultimately the isolated base station fails even for processing all call operations including calls initiated between two subscribers within the same cell associated with the isolated base station. For example, assume that subscriber information associated with HOST_A and HOST_C has been locally stored at BASE-STATION_1, which currently owns the profiles associated with HOST_A and HOST_C. Assume now that the communication link between BASE_STATION_1 and the central database system 14 has failed, and that the profiles associated with HOST_A and HOST_C have been aged out. In this case, BASE_STATION_1 is unable to process any calls associated with HOST_A and HOST_C, including calls initiated between HOST_A and HOST_C.
As mobile communications networks expand with an increasing number of subscribers, coverage areas, and base stations, the conventional fully and partially centralized approaches to managing subscriber profile information, and location information, becomes more problematic and less feasible. Also, the amount of network traffic and network congestion becomes very difficult to handle.
Also, there are emerging plans to implement fully Internet protocol (IP) and to end enabled mobile communications networks wherein each of the base stations communicate via an IP network such as the Internet. The above described problems of network congestion are dependent on a central server associated with centralized cache management systems are even more problematic in an IP network wherein network traffic and congestion must be minimized in order to accommodate a wider variety of applications being supported by the network.
It is an object of the present invention to provide a location update protocol, which reduces the load on the central server/database by reducing queries for subscriber profiles. By reducing the number of queries per minute on the central server, a less powerful and more inexpensive server may be used for the central server site for managing location data.
Briefly, a presently preferred embodiment of the present invention includes a location update protocol for use in a mobile communications network having a distributed cache for managing subscriber profile information associated with each of a plurality of subscribers of the network. The network includes: a plurality of base stations communicatively coupled with each other via a backbone of the network, each of the base stations having an associated coverage area, and being operative to communicate via wireless communication links with subscribers using mobile hosts located within the associated coverage area.
Each of the base stations includes a memory unit having a local database for storing: a local subscriber list including a plurality of locally owned cache entries each having an associated subscriber key value, and an associated locally owned subscriber profile; and a global subscriber list including a plurality of global cache entries each having an associated subscriber key value, and an associated location value indicating a node in the network at which an associated subscriber profile is stored. Each of the base stations is operative to transfer and copy selected ones of the cache entries to other ones of the base stations via the backbone for the purposes of managing and accessing the distributed cache, and for supporting communications applications in the network in accordance with a distributed cache synchronization (DCS) protocol.
Each of the base stations may be operated in accordance with any DCS protocol to transfer a particular one of the cache entries to a new owner one of the base stations via the backbone upon execution of an associated handoff procedure. Each of the base stations is also operative in accordance with the DCS protocol to copy a particular one of the cache entries to a requesting one of the base stations via the backbone in response to receiving a cache entry copy request message from the requesting base station.
Each of the base stations can have an associated mirror base station list indicating at least one associated mirror one of the base stations. The local database of each of the base stations further provides for storage of a mirror subscriber profile list including a plurality of mirror cache entries each having an associated subscriber key value, and an associated mirror subscriber profile. Each of the base stations is operative to periodically transfer mirror copies of each of the associated locally owned cache entries to each of the associated mirror base stations via the back bone in accordance with the protocol. These mirror base stations may be base stations of the adjacent cells.
An important advantage of the location update protocol of the present invention is that it provides reduced dependency on the central database system, increased robustness, and improved fault tolerance in the network.
Another important advantage of the location update protocol of the present invention is that network traffic is reduced as a result of reducing the number of messages and data sent to and from the central database system.
A further advantage of the location update protocol of the present invention is that if ownership of a particular one of the subscriber profiles associated with a particular one of the hosts is transferred from an old one of the base stations to a new mirror base station associated with the old base station as a result of a hand off procedure executed while the particular host is engaged in a communication session controlled by the old base station, then transfer of control of the communication session to the new mirror base station is facilitated by the new mirror base station already having a copy of the particular subscriber profile
Yet another advantage of the location update protocol of the present invention is that less expensive central computer systems may be used at the central database system as a result of reducing the processing requirements of the central computer system.
The foregoing and other objects, features, and advantages of the present invention will be apparent from the following detailed description of the preferred embodiment, which makes reference to the several figures of the drawing.